Communications Bus Data Transmission Using Relative Ground Shifting

ABSTRACT

Methods are described herein for communications bus data transmission using relative ground shifting. A plurality of voltage lines of at least one electronic control unit (ECU) are monitored. The at least one ECU electrically coupled to a communications bus. A voltage differential across at least two of the plurality of voltage lines of the at least one ECU is measured. A pulse or data stream is injected into the communications bus via one or two voltage lines based on the measured voltage differential having an amplitude lower than a predetermined voltage threshold.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation under 35 U.S.C. § 120 of patent application Ser. No. 15/462,611, filed on Mar. 17, 2017, the contents of which are hereby fully incorporated by reference.

BACKGROUND

With the increase in connectivity and data requirements being placed on forms of non-traditional computing platforms, vehicles of different modalities such as planes, trains, motor vehicles, ships, and satellites are exchanging data between themselves and the internet at large. These external communications are known as vehicle-to-vehicle (V2V) communications or vehicle-to-any (V2X) communications. Increase in such communications can pose security risks by exposing the vehicle control networks (VCNs) of these non-traditional computing platforms to potential security breaches and other types of unauthorized access attempts. VCNs having a single point network gateway and/or software based solutions can be susceptible to such security risks remotely. In addition to vehicle applications, there are many other non-vehicle environments which utilize communications buses to send and receive information amongst components within and/or outside. Such applications can range from medical devices to industrial control systems.

SUMMARY

In one aspect, a plurality of voltage lines of at least one ECU are monitored. A voltage differential across at least three of the plurality of voltage lines of the at least one ECU is measured. A data stream is injected into the communications bus via at least two voltage lines based on the measured voltage differential having an amplitude lower than a predetermined voltage threshold.

In some variations, the data stream can be a half-duplex data stream. The predetermined threshold comprises an absolute value of a summation of a first voltage range of one voltage line and a second voltage range of another voltage line.

In another aspect, a plurality of voltage lines of at least one ECU are monitored. A voltage differential across at least two of the plurality of voltage lines of the at least one ECU is measured. A pulse is injected into the communications bus via one of the plurality of voltage lines based on the measured voltage differential having an amplitude lower than a predetermined voltage threshold.

In some variations, the communications bus comprises a serial communications bus. The serial communications bus can be a control area network (CAN) bus having the two of the plurality of voltage lines as either a CAN high voltage line or a CAN low voltage line and a ground line. The predetermined threshold can comprise a voltage range of the one of the plurality of voltage lines. The pulse can comprise a time domain synchronized pulse. Alternatively, the serial communications bus can be a CAN bus having the at least three of the plurality of voltage lines comprising a CAN high voltage line, a CAN low voltage line, and a ground line. The predetermined threshold can comprise an absolute value of a summation of a first voltage range of one voltage line and a second voltage range of another voltage line.

In other variations, a vehicle control network comprises the communications bus. The vehicle control network can include (i) at least one ECU electrically coupled between the communications bus and a plurality of nodes, (ii) at least one security module electrically coupled between the at least one ECU and the communications bus, and (iii) at least a portion of the communications bus.

In some variations, the monitoring is initiated upon at least one of during operation of the at least one security module, after replacement of the at least one security module, during a loss of clock synchronization of the at least one security module, during a predetermined clock synchronization time window, or after replacement of the at least one ECU.

In other variations, the at least one security module comprises a data processor, a microcontroller, one or more transceivers, a clock, a power regulator, a transmitter, and an analog-to-digital (AD) sampler.

In some variations, at least one of a motor vehicle, a ship, an airplane, or a train comprises the communications bus.

Non-transitory computer program products (i.e., physically embodied computer program products) are also described that store instructions, which when executed by one or more data processors of one or more computing systems, cause at least one data processor to perform operations described herein. The memory may temporarily or permanently store instructions that cause at least one processor to perform one or more of the operations described herein. In addition, methods can be implemented by one or more data processors either within a single computing system or distributed among two or more computing systems. Such computing systems can be connected and can exchange data and/or commands or other instructions or the like via one or more connections, including but not limited to a connection over a network (e.g., the Internet, a wireless wide area network, a local area network, a wide area network, a wired network, or the like), via a direct connection between one or more of the multiple computing systems, etc.

The subject matter described herein provides many technical advantages. For example, the current subject matter provides an un-modifiable trusted hardware unit for the analysis and defense of a connected network that compromised controllers which belong to that network may otherwise be unable to access or affect. This platform can be utilized, for example, by vehicle manufacturers to provide a flexible, modular, and scalable security capability for use across their models without the need to design security solutions for each vehicle platform. Moreover, the security platform can utilize encrypted and signed over-the-air (OTA) or V2X communications methods to allow original equipment manufacturers (OEMs) to change or update the security features and capabilities of the vehicle platform without the need to recall the vehicle or change hardware in depot.

The details of one or more variations of the subject matter described herein are set forth in the accompanying drawings and the description below. Other features and advantages of the subject matter described herein will be apparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a system diagram illustrating an example logical system architecture for use in connection with the current subject matter;

FIG. 2 is a system diagram illustrating another example logical system architecture for use in connection with the current subject matter;

FIG. 3 is a system diagram illustrating a logical integration of security module integration with one ECU of a vehicle;

FIG. 4 is an example amplitude versus time plot of an injected data stream on two differential signaling lines;

FIG. 5 is an example amplitude versus time plot of an injected data stream on a single differential signaling line;

FIG. 6 is an example process flow diagram of communications bus data transmission using relative ground comparison techniques; and

FIG. 7 is an example process flow diagram of communications bus data transmission analysis and recovery using microburst transmissions and high-accuracy clocks.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

The current subject matter is directed to techniques for protecting vehicle control and/or communications equipment and networks from alteration or malicious modification, through hardware and software platforms connected to one or more ECUs. A hardware module can be connected to or embedded on the ECU whereby creating a point for communications centralization and security posture assessment. Such a platform can provide defensive capabilities such as communications encryption, attack detection and prevention, ECU fingerprinting and authentication, message modification prevention, message activity recording, and a next-generation firewall. The platform can also provide awareness of an attack or compromise, control communications from the affected module to the network, and defend other ECUs on the network. In addition, the security platform can be used to monitor human-machine interfaces and third party firmware within the vehicle for integrity and malicious modification, reporting this to the user or external security personnel.

FIG. 1 is a system diagram 100 illustrating an example logical system architecture for use in connection with the current subject matter. A network 110 can include one or more ECUs 120. Each ECU 120 can communicate with one or more nodes 130. Nodes 130 can be, for example, external communication nodes (i.e., Bluetooth, Wi-Fi, Cellular, NFC, etc.), and/or vehicle sensors or actuators within the physical boundaries of the vehicle frame. In addition, a vehicle may also utilize connections to OEM or secondary monitoring services over the Internet via nodes 130. Each ECU can be electrically coupled to a communications bus/network interface 140.

The hardware protection framework can be used for a variety of different applications for protection of a network. One example is in connection with motor vehicles. Modern motor vehicles, for example, utilize an on-board diagnostics (OBD) standard to monitor, control, and/or diagnose a variety of vehicle aspects from engine control to accessory components. A CAN bus is a serial communications network bus used by some motor vehicles that allows for microcontrollers and other devices within the vehicle to communicate with one another.

Security zones can be established to provide a protection framework for one or more ECUs 120 and one or more nodes 130. A single security module 150 can be electrically coupled to a single ECU 120. That single ECU 120 can be connected to one or more nodes 130. A security zone can be established by grouping together multiple security modules 150 having a one to one correlation with a corresponding ECU 120 (i.e., security zone Z). Alternatively, a security zone can be established to include a single security module 150 correlated to a single ECU 120 (i.e., security zone Y). Establishing of security zones can occur during installation of the one or more security modules 150 and can be based on the aspects of the security protection framework.

Message traffic on data bus 140 can be encrypted such that the message security zone origination or destination can be identified. For example, the message traffic along communications bus/network interface 140 can identify if the origin of such traffic is from an ECU 120 belonging to security zone X or alternatively from ECU 120 belonging to security zone Y.

In one variation, security module 150 can be integrated within the ECU (not shown). The physical connection between security module 150 and ECU 120 can differ based on the particular ECU being connected. However, the logical connections between security module 150 and ECU 120 can be uniform across varying ECU types.

Alternatively, in another variation, security module 150 can be an external interposer board electrically coupled external to the ECU 120, between the ECU 120 and communications bus/network interface 140. In this variation, the ECU 120 can be physically disconnected from its communication bus 140 connection as security module 150 has a physical connection between the communications bus/network interface 140 and ECU 120.

One or more security modules 150 can communicate with each other via message traffic along path A. Security modules 150 can communication with communications bus/network interface 140 via path B. Each ECU can communicate with its respective connected security module 150 via path C. The communication between one or more security modules 150 can be an out of band communication along communications bus/network interface 140. Path A indicates a logical connection that is routed over the physical communication bus 140. Cross-communication information (i.e., information decipherable by the security modules) between one or more security modules 150 can be exchanged along path A. Path B represents a physical connection to communications bus/network interface 140. Path C indicates a logical connection between one or more security modules 150 and one or more ECUs 120.

FIG. 2 is a system diagram 200 illustrating another example logical system architecture for use in connection with the current subject matter. In some variations, a single security module 150 can be configured to communicate with multiple ECUs 120 using a cryptographic interface of security module 150. This one to many mapping can form part of a security zone (i.e., security zone Z).

FIG. 3 is a system diagram 300 illustrating a logical integration of security module 150 with one ECU of a system 350. Security module 150 can include a variety of components which can monitor, interpret, and/or inject data of communications bus/network interface 140. The components of security module 150 can include, for example, a processor 302, a hashing encryption chip 304, a memory 306, a clock 308, a microcontroller 310, one or more transceivers 312, 316, a failsafe module 314, a power regulator 318, a sideband transmitter 322, and an AD sampler 320. Processor 302 can be a general-purpose security processor that can perform calculations and logic operations required to execute operations described herein. A non-transitory processor-readable storage medium, such as memory 306 which can be an encrypted flash memory, can be in communication with the microcontroller 310 and can include one or more programming instructions for the operations specified herein. For example, memory 306 can store one or more signal fingerprints of ECU 120. Programming instructions can be encrypted using hashing encryption chip 304. Hashing encryption chip 304 can also encrypt message traffic along paths A, B, and/or C. Microcontroller 310 can be regulated by clock 308. Clock 308 can be a high-precision clock that is synchronized based on bus initialization or upon determining that synchronization has been lost. A predetermined time synchronization window can be set for clock 308. Microcontroller 310 can also include a memory (not shown) for performing various operations specified herein.

Microcontroller 310 can receive instructions provided by processor 302 in order to operate the one or more transceivers 312, 316. Transceiver 312 can be a CAN transceiver that receives data bus information from communications bus/network interface 140 that is first filtered through an AD sampler 320. The AD sampler 320 can obtain a high-resolution fingerprint of a sending transceiver of one or more ECUs 120. Transceiver 316 can also be a CAN transceiver. Transceiver 316 can be electrically coupled to the ECU 120 and can received data bus information from communications bus/network interface 140 that is first filtered through an AD sampler 320. Transceivers 314, 316 can be discrete and can each communicate with failsafe module 314. Sideband transmitter 322 can communication with microcontroller 310 and transceiver 312.

Some components of security module 150 can be interconnected with system 350. In one example, system 350 can be a vehicle such as a motor vehicle, plane, train, and/or a ship. System 350 can also be any other non-traditional system having a communications bus/network interface 140. System 350 can include communications bus/network interface 140, one or more ECUs 120, can have a battery voltage (VBAT) 352 and a ground (GND) 354. Transceiver 316 can be electrically coupled to ECU 120 in order to exchange message traffic with ECU 120. AD sampler 320 can be electrically coupled to communications bus/network interface 140. Security module 150 can be powered through electrical couplings with system 350. For example, power regulator 318 can be electrically coupled to the battery voltage 352 and grounded by ground 354. As a result, security module 150 can be operative based on the power provided by the system 350.

FIG. 4 is an example amplitude versus time plot 400 of an injected data stream on two differential signaling lines (i.e., CAN high 410 and CAN low 420). For visual purposes only, the time x-axis of plot 400 is arbitrary and has no associated units. The CAN bus allows for differential signaling on two voltage lines which can include the CAN high and CAN low lines of the bus. The CAN bus also defines the state of bits transferred on the communications bus/network interface 140 to be either dominant (0) or recessive (1). These states correspond to the states of the CAN high and CAN low voltage lines. For example, a relative voltage of CAN low voltage line (i.e., plot line 420) can be 1.5 V for the dominant state. The relative voltage for the dominant state of a CAN high voltage line (i.e., plot line 410) is 3.5 V. For the recessive state, a relative voltage for the CAN low voltage line (i.e., plot line 420) is 2.5 V and the relative voltage for the CAN high voltage line is 2.5 V.

A voltage differential can be measured across the CAN high and CAN low voltage lines relative to a ground line of the ECU 120. Additional data can be injected onto either the CAN high or CAN low voltage lines. While this additional data can be perceived by the CAN bus as noise, one or more security modules 150 can interpret and send data that is essentially transparent to the CAN bus. For example, input data stream 430 can be injected at low speeds and encoded onto an existing CAN bus differential bit stream via either the CAN high 410 or CAN low 420 voltage lines. Data stream 430 can be injected by security module 150 into a CAN bus for a given ECU 120 without adding additional electrical connections to the bus. The injected data can also be within normal signaling voltages of the voltages lines the data is injected into.

In one example, data stream 430 can be a 0.5 V data stream. Data stream 430 can be injected into the CAN high voltage line (i.e., plot line 410) which results in a modifying data stream of the CAN high voltage line as shown in CAN high with data (i.e., plot line 440). Data stream 430 can be made up of, for example, a series of micro-pulses. Similarly, data stream 430 can be injected into the CAN low voltage line (i.e., plot line 420) which results in a modified data stream of the CAN low voltage line as shown in CAN low with data (i.e., plot line 450). By adding in a moderate resolution clock provided by clock 308 and synchronization protocols, both CAN high with data (i.e., plot line 440) and CAN low with data (i.e., plot line 450) are additional half duplex data streams added onto the CAN bus.

The resulting CAN high with data (i.e., plot line 440) and CAN low with data (i.e., plot line 450) data streams operate at a substantially higher frequency than the CAN bus signaling. The resulting data stream(s) provide for a larger tolerance for bus noise at any given point in time. Adding in forward error correction, the bus noise can be addressed by the higher bandwidth of the bit stream to address noise versus the differential signaling mechanism. This can result in preservation of the original content of the CAN bus messaging protocols, while adding an additional data stream 430.

FIG. 5 is an example amplitude versus time plot 500 of an injected data stream on a single differential signaling line. For visual purposes only, the time x-axis of plot 500 is arbitrary and has no associated units. Using time domain synchronized pulses of a lower voltage than the signaling voltage on the CAN bus can provide a way to send information that is outside of the normal signaling mechanism used on the CAN bus. This allows for transferring of a bit stream that is different than the normal bit stream sent across the CAN bus by differential signaling on the CAN high and CAN low lines. The voltage of the micro-pulses is low enough that it does not interfere with the normal signaling on the CAN bus.

Information can be encoded by security module 150 and injected into the CAN bus using low voltage pulses relative to CAN bus ground. The low voltage pulses, for example, can be transmitted at substantially short intervals (i.e., micro-pulses) using a high-precision clock oscillator (i.e., clock 308). The pulses can be encoded using a forward error correction approach by expanding the data message of the existing data stream and inserting accumulative parity information into the pulses such that data loss of over 50% can be tolerated and recovered from. Through incorporating the forward error correction, signal corruption caused by, for example, electrical noise and/or bus line state changes can be accounted for.

For example, a pulse 510 can be injected into the CAN high voltage line (i.e., plot line 520) resulting in a CAN high with data (i.e., plot line 530). The signaling mechanism is also applicable to only one CAN bus line (CAN high or CAN low), but could also be used across both voltage lines to create full-duplex communications.

FIG. 6 is an example process flow diagram 600 of communications bus data transmission using relative ground comparison techniques. A plurality of voltage lines of at least one ECU electrically coupled to a communications bus can be monitored, at 610. A voltage differential can be measured, at 620, across at least three of the plurality of voltage lines of at least one ECU. A ground line can be one of the plurality of voltage lines. A data stream can be injected, at 630, into the communications bus via at least two of the at least three voltage lines based on the measured voltage differential having an amplitude lower than a predetermined voltage threshold. The predetermined threshold can comprise an absolute value of a summation of a first voltage range of a first voltage line and a second voltage range of another voltage line.

FIG. 7 is an example process flow diagram 700 of communications bus data transmission analysis and recovery using microburst transmissions and high-accuracy clocks. A plurality of voltage lines of at least one ECU electrically coupled to a communications bus can be monitored, at 710. A voltage differential can be measured, at 720, across at least two of the plurality of voltage lines of at least one ECU. A pulse can be injected, at 730, into the communications bus via one of the at least two voltage lines based on the measured voltage differential having an amplitude lower than a predetermined voltage threshold. The predetermined threshold can comprise a voltage range of the one of the plurality of voltage lines.

One or more aspects or features of the subject matter described herein can be realized in digital electronic circuitry, integrated circuitry, specially designed application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs) computer hardware, firmware, software, and/or combinations thereof. These various aspects or features can include implementation in one or more computer programs that are executable and/or interpretable on a programmable system including at least one programmable processor, which can be special or general purpose, coupled to receive data and instructions from, and to transmit data and instructions to, a storage system, at least one input device, and at least one output device. The programmable system or computing system can include clients and servers. A client and server are generally remote from each other and typically interact through a communication network. The relationship of client and server arises by virtue of computer programs running on the respective computers and having a client-server relationship to each other.

These computer programs, which can also be referred to as programs, software, software applications, applications, components, or code, include machine instructions for a programmable processor, and can be implemented in a high-level procedural language, an object-oriented programming language, a functional programming language, a logical programming language, and/or in assembly/machine language. As used herein, the term “computer-readable medium” refers to any computer program product, apparatus and/or device, such as for example magnetic discs, optical disks, memory, and Programmable Logic Devices (PLDs), used to provide machine instructions and/or data to a programmable processor, including a computer-readable medium that receives machine instructions as a computer-readable signal. The term “computer-readable signal” refers to any signal used to provide machine instructions and/or data to a programmable processor. The computer-readable medium can store such machine instructions non-transitorily, such as for example as would a non-transient solid-state memory or a magnetic hard drive or any equivalent storage medium. The computer-readable medium can alternatively or additionally store such machine instructions in a transient manner, for example as would a processor cache or other random access memory associated with one or more physical processor cores.

In the descriptions above and in the claims, phrases such as “at least one of” or “one or more of” may occur followed by a conjunctive list of elements or features. The term “and/or” may also occur in a list of two or more elements or features. Unless otherwise implicitly or explicitly contradicted by the context in which it is used, such a phrase is intended to mean any of the listed elements or features individually or any of the recited elements or features in combination with any of the other recited elements or features. For example, the phrases “at least one of A and B;” “one or more of A and B;” and “A and/or B” are each intended to mean “A alone, B alone, or A and B together.” A similar interpretation is also intended for lists including three or more items. For example, the phrases “at least one of A, B, and C;” “one or more of A, B, and C;” and “A, B, and/or C” are each intended to mean “A alone, B alone, C alone, A and B together, A and C together, B and C together, or A and B and C together.” In addition, use of the term “based on,” above and in the claims is intended to mean, “based at least in part on,” such that an unrecited feature or element is also permissible.

The subject matter described herein can be embodied in systems, apparatus, methods, and/or articles depending on the desired configuration. The implementations set forth in the foregoing description do not represent all implementations consistent with the subject matter described herein. Instead, they are merely some examples consistent with aspects related to the described subject matter. Although a few variations have been described in detail above, other modifications or additions are possible. In particular, further features and/or variations can be provided in addition to those set forth herein. For example, the implementations described above can be directed to various combinations and subcombinations of the disclosed features and/or combinations and subcombinations of several further features disclosed above. In addition, the logic flows depicted in the accompanying figures and/or described herein do not necessarily require the particular order shown, or sequential order, to achieve desirable results. Other implementations may be within the scope of the following claims. 

What is claimed is:
 1. A method for implementation by one or more data processors forming one or more computing devices, the method comprising: monitoring, by at least one data processor of at least one security module, a plurality of voltage lines of at least one electronic control unit (ECU) electrically coupled to a communications bus; measuring, by at least one data processor, a voltage differential across at least three of the plurality of voltage lines of the at least one ECU; and injecting, by at least one data processor, a data stream into the communications bus via at least two voltage lines of the at least three measured voltage lines based on the measured voltage differential having an amplitude lower than a predetermined voltage threshold.
 2. The method according to claim 1, wherein the communications bus comprises a serial communications bus.
 3. The method according to claim 2, the serial communications bus comprises a controller area network (CAN) bus and wherein the at least three of the plurality of voltage lines comprises a CAN high voltage line, a CAN low voltage line, and a ground line.
 4. The method according to claim 1, wherein the predetermined threshold comprises an absolute value of a summation of a first voltage range of one voltage line and a second voltage range of another voltage line.
 5. The method according to claim 1, wherein the data stream comprises a half-duplex data stream.
 6. The method according to claim 1, wherein a vehicle control network comprises the communications bus, the vehicle control network comprising (i) the at least one ECU electrically coupled between the communications bus and a plurality of nodes, (ii) the at least one security module electrically coupled between the at least one ECU and the communications bus, and (iii) at least a portion of the communications bus.
 7. The method according to claim 1, wherein the monitoring is initiated upon at least one of: during operation of the at least one security module, after replacement of the at least one security module, during a loss of clock synchronization of the at least one security module, during a predetermined clock synchronization time window, or after replacement of the at least one ECU.
 8. The method according to claim 1, wherein the at least one security module comprises a data processor, a microcontroller, one or more transceivers, a clock, a power regulator, a transmitter, and an analog-to-digital (AD) sampler.
 9. The method according to claim 1, wherein at least one of a motor vehicle, a ship, an airplane, or a train comprises the communications bus.
 10. The method according to claim 1 further comprising: receiving, by at least one data processor of another security module, the injected data stream; and determining, by at least one data processor, cross-communication information between the at least one security module and the another security module based on a plurality of micro-pulses within the injected data stream.
 11. A method for implementation by one or more data processors forming one or more computing devices, the method comprising: monitoring, by at least one data processor of at least one security module, a plurality of voltage lines of at least one electronic control unit (ECU) electrically coupled to a communications bus; measuring, by at least one data processor, a voltage differential across at least two of the plurality of voltage lines of the at least one ECU; and injecting, by at least one data processor, a pulse into the communications bus via one of the plurality of voltage lines based on the measured voltage differential having an amplitude lower than a predetermined voltage threshold.
 12. The method according to claim 11, wherein the communications bus comprises a controller area network (CAN) bus and wherein the at least two of the plurality of voltage lines comprises either a CAN high voltage line or a CAN low voltage line and a ground line.
 13. The method according to claim 11, wherein the predetermined threshold comprises a voltage range of the one of the plurality of voltage lines.
 14. The method according to claim 11, wherein the pulse comprises a time domain synchronized micro-pulse.
 15. The method according to claim 11, wherein a vehicle control network comprises the communications bus, the vehicle control network comprising (i) the at least one ECU electrically coupled between the communications bus and a plurality of nodes, (ii) the at least one security module electrically coupled between the at least one ECU and the communications bus, and (iii) at least a portion of the communications bus.
 16. The method according to claim 11, wherein the monitoring is initiated upon at least one of: during operation of the security module, after replacement of the at least one security module, during a loss of clock synchronization of the at least one security module, during a predetermined clock synchronization time window, or after replacement of the at least one ECU.
 17. The method according to claim 11, wherein the at least one security module comprises a data processor, a microcontroller, one or more transceivers, a clock, a power regulator, a transmitter, and an analog-to-digital (AD) sampler.
 18. The method according to claim 11, wherein at least one of a motor vehicle, a ship, an airplane, or a train comprises the communications bus.
 19. The method according to claim 11 further comprising: receiving, by at least one data processor of another security module, the injected data stream; and determining, by at least one data processor, cross-communication information between the at least one security module and the another security module based on the injected pulse within a data stream.
 20. A vehicle control network comprising: a communications bus; at least one electronic control unit (ECU) electrically coupled to the communications bus each having a plurality of voltage lines; at least one security module; wherein: the at least one security module monitors the plurality of voltage lines of the at least one ECU; a voltage differential is measured across at least three of the plurality of voltage lines of the at least one ECU; a data stream is injected into the communications bus via at least two voltage lines of the at least three measured voltage lines based on the measured voltage differential having an amplitude lower than a predetermined voltage threshold; the at least one ECU is electrically coupled between the communications bus and a plurality of nodes; and the at least one security module is electrically coupled between the at least one ECU and the communications bus.
 21. A system comprising: means for monitoring a plurality of voltage lines of at least one electronic control unit (ECU) electrically coupled to a communications bus; means for measuring a voltage differential across at least two of the plurality of voltage lines of the at least one ECU; and means for injecting a pulse into the communications bus via one of the plurality of voltage lines based on the measured voltage differential having an amplitude lower than a predetermined voltage threshold. 